In wireless communications, a wireless communication device is subject to failures, such as a reduced received signal level (RSL), increased bit errors, and interrupted communications, caused by a natural phenomenon, equipment failure, or the like. Concerning failures on a wireless line, there may appear a sign of fading or other failure causes. Detecting such sign of a failure cause in advance and proactively dealing with the failure cause can reduce failures before they occur.
In relation to the above-described art, PTL 1, for example, discloses a wireless device that identifies the cause of failure on a wireless link with another wireless station to take a countermeasure. The wireless device according to PTL 1 obtains characteristic values of statistical information representing the state of the wireless link, and detects, in a predetermined order and based on the characteristic values, a plurality of causes of failure associated in advance with statistical information. In addition, the wireless device according to PTL 1 takes the countermeasures associated with the detected causes of failure. According to PTL 1, the plurality of causes of failure include the presence of: shadowing, radio noise, multi-path fading, heavy traffic, and a hidden terminal. The detection in a predetermined order refers to detecting the presence of shadowing, followed by detecting the presence of radio noise, and further detecting the presence of multi-path fading, heavy traffic, and a hidden terminal in a predetermined order.
As another example, PTL 2 discloses a technique to detect and notify an abnormality of equipment or a line by using a space diversity in-phase combining board (SD COMB board) that is used for a multiplex wireless device. The SD COMB board includes: first and second signal distributors that branch an input signal into two signals; a phase shifter that adjusts the phase of a signal inputted based on a control signal; first and second AGC amplifiers that control gains so as to have a constant amplitude; and a phase comparison mixer that multiplies an output signal of the first AGC amplifier by an output signal of the second AGC amplifier and outputs a phase comparison result signal that indicates the phase difference. The SD COMB board further includes: a control circuit that outputs a control signal according to the phase comparison result signal; first and second detection circuits that output first and second detection signals indicating the presence or absence of an input signal; a third detection circuit that detects an abnormality of equipment or an input signal based on the phase comparison result signal and on the first and second detection signals; and a warning means that displays an abnormality of equipment or an input signal based on the detection result produced by the third detection circuit.